1. Field of the Invention
The present invention relates to a suspension device for mobile self-lift drilling platforms.
2. Description of the Prior Art
Different methods are known for suspending a self-lift platform.
A first solution is represented by an elastomer device with laminated structure, namely comprising a stack of elastomer layers of appropriate thickness alternating with metal plates, to which they are adhered.
This laminated structure, which is resilient and so deformable, is intended to cooperate with a reduction system for raising and lowering the legs (or feet) of the self-lift platform, which system is of the rack and pinion type and is contained in a floating enclosure (several racks are integral with the same leg platform).
This laminated elastic structure is remarkable in that it withstands not only axial forces but also lateral forces.
A second solution uses a thick wall cushion (or pad) made from elastomer reinforced by means of high tensile strength steel wires, which cushion defines a deformable chamber intended to be filled with a pressurized liquid, such as a water and glycol solution for use at low temperatures. Each cushion of this type is connected (independently or jointly with the other cushions associated with the same leg of the platform) to a hydraulic accumulator for improving the shock absorption capacity.
By means of a pressure gauge, the load acting on the cushions and transmitted thereto by the legs of the platform may be checked, which further allows, on the one hand, the distribution of the loads supported by the different legs of the platform to be checked and, on the other hand, any variation of load due for example to the accidental sinking of a leg into a weakly resistant sea bed to be immediately detected and measured.
Each cushion or pad is further disposed between two metal plates for limiting its axial deformation, the transverse or lateral deformation being limited by axial projections on each plate;
The above described deformable hydraulic cushion may be used in place of said laminated elastic structure or in cooperation therewith.
(A third solution is also known which comprises the use of a system of connecting rods, but which is outside the scope of the present invention).
Now, it should be noted, particularly in so far as the deformable hydraulic cushion is concerned, that--although it is theoretically intended to replace said laminated elastic structure--in actual fact the cooperation between these two devices is, in practice, imperative because the suspension cushion is not adapted to withstand the lateral forces, whereas the laminated structure is capable of so doing.
It should be further noted that, because of the totally deformable structure of the suspension cushion, it is not capable of withstanding, for equal liquid pressure, the same load when--because of an imbalance of the platform (as can be verified, for example, in the case of accidental sinking of one or more legs of the platform into the sea bed)--the cushion increases in volume (in the case of said example, it is a question of the cushions associated with the leg or legs which are not concerned by the sinking): in fact, in this case the contact surface with said plates, which limit its axial deformation, decreases and consequently the force or load which it may support (the pressure being the same) decreases so that, for supporting the same load, the pressure would have to be increased as a function of the deformation, which is absolutely unthinkable with this hydraulic cushion.